key is just a variable name.
for key in d:
will simply loop over the keys in the dictionary, rather than the keys and values. To loop over both key and value you can use the following:
For Python 3.x:
for key, value in d.items():
For Python 2.x:
for key, value in d.iteritems():
To test for yourself, change the word key to poop.
In Python 3.x, iteritems() was replaced with simply items(), which returns a set-like view backed by the dict, like iteritems() but even better.
This is also available in 2.7 as viewitems().
The operation items() will work for both 2 and 3, but in 2 it will return a list of the dictionary's (key, value) pairs, which will not reflect changes to the dict that happen after the items() call. If you want the 2.x behavior in 3.x, you can call list(d.items()).
key is just a variable name.
for key in d:
will simply loop over the keys in the dictionary, rather than the keys and values. To loop over both key and value you can use the following:
For Python 3.x:
for key, value in d.items():
For Python 2.x:
for key, value in d.iteritems():
To test for yourself, change the word key to poop.
In Python 3.x, iteritems() was replaced with simply items(), which returns a set-like view backed by the dict, like iteritems() but even better.
This is also available in 2.7 as viewitems().
The operation items() will work for both 2 and 3, but in 2 it will return a list of the dictionary's (key, value) pairs, which will not reflect changes to the dict that happen after the items() call. If you want the 2.x behavior in 3.x, you can call list(d.items()).
It's not that key is a special word, but that dictionaries implement the iterator protocol. You could do this in your class, e.g. see this question for how to build class iterators.
In the case of dictionaries, it's implemented at the C level. The details are available in PEP 234. In particular, the section titled "Dictionary Iterators":
Dictionaries implement a tp_iter slot that returns an efficient iterator that iterates over the keys of the dictionary. [...] This means that we can write
for k in dict: ...which is equivalent to, but much faster than
for k in dict.keys(): ...as long as the restriction on modifications to the dictionary (either by the loop or by another thread) are not violated.
Add methods to dictionaries that return different kinds of iterators explicitly:
for key in dict.iterkeys(): ... for value in dict.itervalues(): ... for key, value in dict.iteritems(): ...This means that
for x in dictis shorthand forfor x in dict.iterkeys().
In Python 3, dict.iterkeys(), dict.itervalues() and dict.iteritems() are no longer supported. Use dict.keys(), dict.values() and dict.items() instead.
Iterate through a Dictionary
What is the fastest way to iterate over a dictionary?
Why do you need to apply the method .items() to iterate over a dictionary?
How to slice a dictionary
I’m stumped on how to iterate through a dictionary and compare each keys value to one another. I’m able to compare the first key value to the rest of the keys in the dictionary but after that, comparing say the third key to the first key all in the same loop seems impossible to me as of now.
I’m sure it all goes in a loop starting with:
for keys in ngrams.keys():
basically I’m trying to pull the keys with values who equal the highest (simplified version) and grab those two keys from the rest.
Any tips would be appreciated!